The present invention relates to free piston Stirling cycle engines and more particularly to those which transmit mechanical energy between the power piston and a device or devices positioned outside a gas-containing chamber defined by the engine housing.
The operation of a free piston Stirling engine depends upon, among other things, the maintenance of a gas-containing bounce or reference space in communication with a power piston. If power is to be transmitted by mechanical means, however, the power piston must be accessible from a position outside this gas-containing chamber so that the mechanical means can link the power piston to a device outside the engine. Hence, a gas-tight seal must be provided around a moving object extending through the engine housing.
U.S. Pat. No. 3,937,018 issued Feb. 10, 1976 to the present inventor discloses a simple, rolling or bellows type seal extending inwardly from the housing in surrounding relation to a linearly reciprocative piston rod. A major drawback of the seal is the loss of flexibility which results when its strength or durability is increased. In the present invention, however, a torsionally flexible seal surrounds a rotationally reciprocative drive shaft. This combination permits the seal to be internally reinforced, and consequently more durable, without dampening substantially the stroke of the power piston.
U.S. Pat. No. 3,664,202 issued May 23, 1972 to Metzger discloses a composite torsion tube which provides a gas-tight seal between an oscillatory shaft which it surrounds and the wall of a chamber under pressure. The Metzger torsion tube may be provided, as illustrated, with structurally weakened internal layers, whereas the present invention has at least one intermediate layer of reinforcing material bonded between relatively opposing layers of elastic material.
The problem in a Stirling engine of the type described is to provide a seal which is elastic enough to permit multiple repetitions of substantial angular reciprocation of a shaft extending through a wall and yet stiff enough to resist a high gas pressure tending to force it out of the wall.